When building animations in Java applets, the traditional approach is to load a number of GIF files into memory and then to draw them to the screen one after another. GIF files are used in Internet applications because they give excellent compression (up to about 10 times) for 256 and 16 colour graphics. Because of the compression routine used, decompression requires time. In order to ensure that a GIF can be drawn to screen instantly as required by the animation sequence, GIFs are prepared for rendering by decompressing them to a standard Java Image object. The problem is exacerbated because Java Images are stored as 32 bit RGB+alpha channel images. This means that a single frame of an animation can expand up to 40 times the size of the original GIF file. On typical personal computers this memory glut causes the system to start to page memory to the disk drive which in turn causes poor animation performance.
Throughout this document, the term “movie” is used to denote a computer animation.